Microwave level gauge, or radar level gauge (RLG), systems are in wide use for determining the filling level of a product contained in a tank. Radar level gauging is generally performed either by means of non-contact measurement, whereby electromagnetic signals are radiated towards the product contained in the tank, or by means of contact measurement, often referred to as guided wave radar (GWR), whereby electromagnetic signals are guided towards and into the product by a probe acting as a guided wave transmission line.
Such a probe is generally arranged to extend vertically from the top towards the bottom of the tank. The probe may also be arranged in a measurement tube, a so-called chamber, which is connected to the outer wall of the tank and is in fluid connection with the inside of the tank. Typically, the probe extends from a transmitter/receiver assembly into the product inside the tank, or chamber, via a sealing arrangement which may form a hermetic barrier.
The most common type of guided wave radar uses short pulses (around 1 ns) without carrier and occupy a frequency range of roughly 0.1-1 GHz.
Document U.S. Pat. No. 7,255,002 describes such a guided wave radar level gauge for measuring a level of process material in a tank having an improved sealing arrangement comprising a ceramic seal body which is sealingly joined via brazing on its outer surface to a housing such that the conductor is sealed from the tank atmosphere.
Under some conditions moisture and condensation may enter any gaps formed between the ceramic seal body and the surrounding surfaces. Such moisture or condensation may disturb the reception of the reflected signals such that quality and durability of determination and measurement of the product level is reduced. Such problems may be present for example if the gauge is exposed to high pressure, thus forcing tank atmosphere into the gaps. However, a temperature gradient throughout the sealing arrangement may be sufficient to cause problems with condensation in the gaps, also in a situation without high pressure,